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1
Ronchin, Erika, Timothy Masterlark, John Dawson, Steve Saunders, and Joan Martì Molist. "Imaging the complex geometry of a magma reservoir using FEM-based linear inverse modeling of InSAR data: application to Rabaul Caldera, Papua New Guinea." Geophysical Journal International 209, no. 3 (March 24, 2017): 1746–60. http://dx.doi.org/10.1093/gji/ggx119.
Повний текст джерелаАнотація:
Summary We test an innovative inversion scheme using Green's functions from an array of pressure sources embedded in finite-element method (FEM) models to image, without assuming an a-priori geometry, the composite and complex shape of a volcano deformation source. We invert interferometric synthetic aperture radar (InSAR) data to estimate the pressurization and shape of the magma reservoir of Rabaul caldera, Papua New Guinea. The results image the extended shallow magmatic system responsible for a broad and long-term subsidence of the caldera between 2007 February and 2010 December. Elastic FEM solutions are integrated into the regularized linear inversion of InSAR data of volcano surface displacements in order to obtain a 3-D image of the source of deformation. The Green's function matrix is constructed from a library of forward line-of-sight displacement solutions for a grid of cubic elementary deformation sources. Each source is sequentially generated by removing the corresponding cubic elements from a common meshed domain and simulating the injection of a fluid mass flux into the cavity, which results in a pressurization and volumetric change of the fluid-filled cavity. The use of a single mesh for the generation of all FEM models avoids the computationally expensive process of non-linear inversion and remeshing a variable geometry domain. Without assuming an a-priori source geometry other than the configuration of the 3-D grid that generates the library of Green's functions, the geodetic data dictate the geometry of the magma reservoir as a 3-D distribution of pressure (or flux of magma) within the source array. The inversion of InSAR data of Rabaul caldera shows a distribution of interconnected sources forming an amorphous, shallow magmatic system elongated under two opposite sides of the caldera. The marginal areas at the sides of the imaged magmatic system are the possible feeding reservoirs of the ongoing Tavurvur volcano eruption of andesitic products on the east side and of the past Vulcan volcano eruptions of more evolved materials on the west side. The interconnection and spatial distributions of sources correspond to the petrography of the volcanic products described in the literature and to the dynamics of the single and twin eruptions that characterize the caldera. The ability to image the complex geometry of deformation sources in both space and time can improve our ability to monitor active volcanoes, widen our understanding of the dynamics of active volcanic systems and improve the predictions of eruptions.
2
Nakagawa, Mitsuhiro, and Ken-ichiro Aoki. "Petrology of Moriyoshi volcano - Magma mixing event after caldera collapse." Journal of the Japanese Association of Mineralogists, Petrologists and Economic Geologists 80, no. 4 (1985): 136–54. http://dx.doi.org/10.2465/ganko1941.80.136.
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Robin, Claude, and Alain Potrel. "Multi-stage magma mixing in the pre-caldera series of Fuego de Colima volcano." Geofísica Internacional 32, no. 4 (October 1, 1993): 605–15. http://dx.doi.org/10.22201/igeof.00167169p.1993.32.4.606.
Повний текст джерелаАнотація:
Datos geoquímicos y petrográficos acerca de las lavas anteriores de la caldera del Volcán de Fuego de Colima indican dos procesos magmáticos; cristalización fraccionada y mezcla de magma. Estos procesos pudieron suceder juntos, de tal manera que sus efectos se adicionan. Se distinguen tres tipos de mezcla: (i): mezcla entre nuevas inyecciones de magma profundo y minerales máficos acumulados en la parte inferior de la cámara magmática somera (ii): Mezcla, en la cámara, entre este magma juvenil (anteriormente diferenciado o no en una cámara más profunda, contaminando por olivino y clinopiroxeno o no) y un magma diferenciado de composición andesítica o dacítica. (iii) Mezcla por convección entre magmas ya diferenciados, por separación de minerales, o mezcla, o por ambos procesos, a diferentes niveles en la cámara somera.
4
Clarke, L. B., and M. J. Le Bas. "Magma mixing and metasomatic reaction in silicate-carbonate liquids at the Kruidfontein carbonatitic volcanic complex, Transvaal." Mineralogical Magazine 54, no. 374 (March 1990): 45–56. http://dx.doi.org/10.1180/minmag.1990.054.374.04.
Повний текст джерелаАнотація:
AbstractThe Kruidfontein volcanic complex is a Proterozoic collapsed carbonatitic caldera structure, the inner caldera of which is filled with carbonatitic bedded volcaniclastic rocks cut by carbonatite dykes, and the outer with bedded silicate tuffs. As well as numerous fragments of phonolitic pumice in the silicate tuffs, there are unusual banded fragments composed of alternating silicate and carbonate compositions which appear to have been originally glasses, and which give evidence for mechanical mixing of magmas which may originally have been magmas separated by liquid immiscibility. The fragments have also been strongly fenitized with the introduction of K and the replacement of Al by Fe.
5
Hübner, Marcel, Christoph Breitkreuz, Alexander Repstock, Bernhard Schulz, Anna Pietranik, Manuel Lapp, and Franziska Heuer. "Evolution of the Lower Permian Rochlitz volcanic system, Eastern Germany: reconstruction of an intra-continental supereruption." International Journal of Earth Sciences 110, no. 6 (July 14, 2021): 1995–2020. http://dx.doi.org/10.1007/s00531-021-02053-5.
Повний текст джерелаАнотація:
AbstractExtensional tectonics in the Late Paleozoic Central Europe was accompanied by rift magmatism that triggered voluminous intracontinental caldera-forming eruptions. Among these, the Lower Permian Rochlitz Volcanic System (RVS) in the North Saxon Volcanic Complex (Eastern Germany, Saxony) represents a supereruption (VEI 8, estimated volume of 1056 km3) of monotonous rhyolites followed by monotonous intermediates. Mapping, petrography, whole-rock geochemistry along with mineral chemistry and oxygen isotopes in zircon display its complex eruption history and magma evolution. Crystal-rich (> 35 vol%), rhyolitic Rochlitz-α Ignimbrite with strong to moderate welding compaction erupted in the climactic stage after reheating of the magma by basaltic injections. Due to magma mixing, low-volume trachydacitic-to-rhyolitic Rochlitz-β Ignimbrite succeeded, characterized by high Ti and Zr-values and zircon with mantle δ18O. Randomly oriented, sub-horizontally bedded fiamme, and NW–SE striking subvolcanic bodies and faults suggest pyroclastic fountaining along NW–SE-oriented fissures as the dominant eruption style. Intrusion of the Leisnig and the Grimma Laccoliths caused resurgence of the Rochlitz caldera forming several peripheral subbasins. In the post-climactic stage, these were filled with lava complexes, ignimbrites and alluvial to lacustrine sediments. Significant Nb and Ta anomalies and high Nb/Ta ratios (11.8–17.9) display a high degree of crustal contamination for the melts of the RVS. Based on homogenous petrographic and geochemical composition along with a narrow range of δ18O in zircon Rochlitz-α Ignimbrite were classified as monotonous rhyolites. For the Rochlitz-β Ignimbrites, underplating and mixing with basic melts are indicated by Mg-rich annite–siderophyllite and δ18O < 6.0 in zircon. The wide spectrum of δ18O on zircon suggests an incomplete mixing process during the formation of monotonous intermediates in the RVS.
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Bouvet de Maisonneuve, C., F. Costa, H. Patia, and C. Huber. "Mafic magma replenishment, unrest and eruption in a caldera setting: insights from the 2006 eruption of Rabaul (Papua New Guinea)." Geological Society, London, Special Publications 422, no. 1 (2015): 17–39. http://dx.doi.org/10.1144/sp422.2.
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Lipman, Peter W. "Evolution of silicic magma in the upper crust: the mid-Tertiary Latir volcanic field and its cogenetic granitic batholith, northern New Mexico, U.S.A." Earth and Environmental Science Transactions of the Royal Society of Edinburgh 79, no. 2-3 (1988): 265–88. http://dx.doi.org/10.1017/s0263593300014279.
Повний текст джерелаАнотація:
ABSTRACTStructural and topographic relief along the eastern margin of the Rio Grande rift, northern New Mexico, provides a remarkable cross-section through the 26-Ma Questa caldera and cogenetic volcanic and plutonic rocks of the Latir field. Exposed levels increase in depth from mid-Tertiary depositional surfaces in northern parts of the igneous complex to plutonic rocks originally at 3–5 km depths in the S. Erosional remnants of an ash-flow sheet of weakly peralkaline rhyolite (Amalia Tuff) and andesitic to dacitic precursor lavas, disrupted by rift-related faults, are preserved as far as 45 km beyond their sources at the Questa caldera. Broadly comagmatic 26 Ma batholithic granitic rocks, exposed over an area of 20 by 35 km, range from mesozonal granodiorite to epizonal porphyritic granite and aplite; shallower and more silicic phases are mostly within the caldera. Compositionally and texturally distinct granites define resurgent intrusions within the caldera and discontinuous ring dikes along its margins; a batholithic mass of granodiorite extends 20 km S of the caldera and locally grades vertically to granite below its flat-lying roof. A negative Bouguer gravity anomaly (15–20 mgal), which encloses exposed granitic rocks and coincides with boundaries of the Questa caldera, defines boundaries of the shallow batholith, emplaced low in the volcanic sequence and in underlying Precambrian rocks. Palaeomagnetic pole positions indicate that successively crystallised granitic plutons cooled through Curie temperatures during the time of caldera formation, initial regional extension, and rotational tilting of the volcanic rocks. Isotopic ages for most intrusions are indistinguishable from the volcanic rocks. These relations indicate that the batholithic complex broadly represents the source magma for the volcanic rocks, into which the Questa caldera collapsed, and that the magma was largely liquid during regional tectonic disruption.Volcanic and plutonic magmas (1) changed from early high-K calc-alkaline to alkalic prior to caldera eruptions; (2) differentiated to a weakly peralkaline rhyolite and equivalent acmiteartvedsonite granite cap (underlain by calc-alkaline granite) when the caldera formed at 26·5 Ma; then (3) reverted to calc-alkaline compositions. Concentrations of alkalis and minor elements such as Rb, Th, U, Nb, Zr, and Y reached maxima at the caldera stage. The volcanic rocks constitute intermittently quenched samples of upper parts of Questa magma bodies at early stages of crystallisation; in contrast, the comagmatic granitic rocks preserve an integrated record of protracted crystallisation of the magmatic residue as eruptions diminished. Multiple differentiation processes were active during evolution of the Questa magmatic system: crystal fractionation, replenishment by mantle and lower crustal melts of varying chemical and isotopic character, mixing of evolved with more primitive magmas, upper crustal assimilation, and perhaps volatile-transfer processes. As a result, an evolving batholithic cluster of coalesced magma chambers generated diverse assemblages of broadly cogenetic rocks within a few million years. Evolution of the Questa magmatic system and similar high-level Tertiary granitic batholiths nearby in the southern Rocky Mountains provides broad insights into magmatic processes in continental regions such as the overall shapes of batholiths, time and compositional relations between cogenetic volcanic and plutonic rocks, density equilibration of magmas with country rocks, and thermal evolution of continental crust.
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Deering, Chad D., Thomas A. Vogel, Lina C. Patino, and Guillermo E. Alvarado. "Origin of distinct silicic magma types from the Guachipelín Caldera, NW Costa Rica: Evidence for magma mixing and protracted subvolcanic residence." Journal of Volcanology and Geothermal Research 165, no. 3-4 (September 2007): 103–26. http://dx.doi.org/10.1016/j.jvolgeores.2007.05.004.
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Takashima, Shino, Yutaka Wada, and Hironao Shinjoe. "Miyanotani composite dike in central Kii Peninsula, southwest Japan: Implications for magma mixing and caldera volcanism." Journal of the Geological Society of Japan 116, no. 9 (2010): 496–509. http://dx.doi.org/10.5575/geosoc.116.496.
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Macdonald, R., B. Bagiński, B. G. J. Upton, P. Dzierżanowski, W. Marshall-Roberts, and M. Prieto. "The Palaeogene Eskdalemuir dyke, Scotland: long-distance lateral transport of rhyolitic magma in a mixed-magma intrusion." Mineralogical Magazine 73, no. 2 (April 2009): 285–300. http://dx.doi.org/10.1180/minmag.2009.073.2.285.
Повний текст джерелаАнотація:
AbstractThe Palaeogene Eskdalemuir dyke, part of the Mull dyke swarm in the Southern Uplands of Scotland, is ~60 km long and up to 40 m thick. Its southern tip is 230 km from the inferred source on Mull. The dyke is composite, with tholeiitic basaltic margins and a vitreous central facies ranging from basaltic andesite to andesite in composition. Plagioclase and pyroxene phenocrysts and matrix crystals in the central facies show unusually large compositional ranges and complex textural relationships. Wholerock major and trace-element abundances show linear variations against MgO content, consistent with the rocks in the central facies having formed by mixing of basalt and rhyolite magmas. The rhyolite can be closely matched by rocks from the Mull centre. The mafic and silicic magmas were intruded from a compositionally zoned chamber beneath Mull, perhaps during collapse of the Centre 1 caldera. The lower-viscosity basaltic magma was emplaced before, but lubricated the lateral propagation of, the silicic magma, which mixed with the partially solidified basalt, the proportion of rhyolite increasing towards the dyke centre. The Eskdalemuir dyke represents an unusual, perhaps unique, example of a rhyolite magma being emplaced >200 km from its inferred source. The supposed correlative of the Eskdalemuir dyke north of the Southern Uplands Fault, the Dalraith-Linburn dyke, is not comagmatic with it.
11
Sosa-Ceballos, Giovanni, James E. Gardner, Claus Siebe, and José L. Macías. "A caldera-forming eruption ~14,10014Cyr BP at Popocatépetl volcano, México: Insights from eruption dynamics and magma mixing." Journal of Volcanology and Geothermal Research 213-214 (February 2012): 27–40. http://dx.doi.org/10.1016/j.jvolgeores.2011.11.001.
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de Silva, S. L., J. Roberge, L. Bardelli, W. Báez, A. Ortiz, J. G. Viramonte, J. M. Arnosio, and R. Becchio. "Magmatic evolution and architecture of an arc-related, rhyolitic caldera complex: The late Pleistocene to Holocene Cerro Blanco volcanic complex, southern Puna, Argentina." Geosphere 18, no. 2 (January 25, 2022): 394–423. http://dx.doi.org/10.1130/ges02294.1.
Повний текст джерелаАнотація:
Abstract Through the lens of bulk-rock and matrix glass geochemistry, we investigated the magmatic evolution and pre-eruptive architecture of the siliceous magma complex beneath the Cerro Blanco volcanic complex, a Crater Lake–type caldera complex in the southern Puna Plateau of the Central Andes of Argentina. The Cerro Blanco volcanic complex has been the site of two caldera-forming eruptions with volcanic explosivity index (VEI) 6+ that emplaced the ca. 54 ka Campo Piedra Pomez ignimbrite and the ca. 4.2 ka Cerro Blanco ignimbrite. As such, it is the most productive recent explosive volcano in the Central Andes. The most recent eruptions (younger than 4.2 ka) are dominantly postcaldera effusions of crystal-rich domes and associated small explosive pulses. Previous work has demonstrated that andesitic recharge of and mixing with rhyolitic magma occurred at the base of the magma complex, at ~10 km depth. New isotopic data (Sr, Nd, Pb, and O) confirm that the Cerro Blanco volcanic complex rhyolite suite is part of a regional southern Puna, arc-related ignimbrite group. The suite defines a tight group of consanguineous siliceous magmas that serves as a model for the evolution of arc-related, caldera-forming silicic magma systems in the region and elsewhere. These data indicate that the rhyolites originated through limited assimilation of and mixing with upper-crustal lithologies by regional basaltic andesite parent materials, followed by extensive fractional crystallization. Least squares models of major elements in tandem with Rayleigh fractionation models for trace elements reveal that the internal variations among the rhyolites through time can be derived by extensive fractionation of a quartz–two feldspar (granitic minimum) assemblage with limited assimilation. The rare earth element character of local volumes of melt in some samples of the Campo Piedra Pomez ignimbrite basal fallout requires significant fractionation of amphibole. The distinctive major- and trace-element characteristics of bulk rock and matrix of the Campo Piedra Pomez and Cerro Blanco tephras provide useful geochemical fingerprints to facilitate regional tephrochronology. Available data indicate that rhyolites from other neighborhood centers, such as Cueros de Purulla, share bulk chemical characteristics with the Campo Piedra Pomez ignimbrite rhyolites, but they appear to be isotopically distinct. Pre-eruptive storage and final equilibration of the rhyolitic melts were estimated from matrix glass compositions projected onto the haplogranitic system (quartz-albite-orthoclase-H2O) and using rhyolite-MELTS models. These revealed equilibration pressures between 360 and 60 MPa (~10–2 km depth) with lowest pressures in the Holocene eruptions. Model temperatures for the suite ranged from 695 to 790 °C. Integrated together, our results reveal that the Cerro Blanco volcanic complex is a steady-state (low-magmatic-flux), arc-related complex, standing in contrast to the flare-up (high-magmatic-flux) supervolcanoes that dominate the Neogene volcanic stratigraphy. The silicic magmas of the Cerro Blanco volcanic complex were derived more directly from mafic and intermediate precursors through extensive fractional crystallization, albeit with some mixing and assimilation of local basement. Geochemical models and pressure-temperature estimates indicate that significant volumes of remnant cumulates of felsic and intermediate composition should dominate the polybaric magma complex beneath the Cerro Blanco volcanic complex, which gradually shallowed through time. Evolution to the most silicic compositions and final equilibration of some of the postcaldera domes occurred during ascent and decompression at depths less than 2 km. Our work connotes an incrementally accumulated (over at least 54 k.y.), upper-crustal pluton beneath the Cerro Blanco volcanic complex between 2 and 10 km depth. The composition of this pluton is predicted to be dominantly granitic, with deeper parts being granodioritic to tonalitic. The progressive solidification and eventual contraction of the magma complex may account for the decades of deflation that has characterized Cerro Blanco. The presently active geothermal anomaly and hydrothermal springs indicate the Cerro Blanco volcanic complex remains potentially active.
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Rooyakkers, Shane M., John Stix, Kim Berlo, and Simon J. Barker. "Emplacement of unusual rhyolitic to basaltic ignimbrites during collapse of a basalt-dominated caldera: The Halarauður eruption, Krafla (Iceland)." GSA Bulletin 132, no. 9-10 (January 13, 2020): 1881–902. http://dx.doi.org/10.1130/b35450.1.
Повний текст джерелаАнотація:
Abstract Deposits of the ca. 110 ka Halarauður eruption of Krafla caldera (reconstructed volume = 7 ± 6 km3 dense rock equivalent) include the only spatter-rich ignimbrite known in Iceland, and an exceptionally rare lava-like basaltic ignimbrite. We present a revised stratigraphy and new whole-rock major-element data set for products of this unusual event, one of only three Quaternary ignimbrite eruptions identified in Iceland. Compositions of Halarauður products span a broad range (50.0–74.6 wt% SiO2), reflecting mixing of rhyolite with underplating basalt. Small-volume, valley-ponded, basal pumice- and spatter-bearing lithic breccias and ignimbrite (rhyolite to andesite) reflect rapid column collapse during early opening of ring-fault vents. A transition to voluminous, regionally dispersed spatter agglomerates (dacite to basaltic andesite) marks an abrupt eruptive intensification, as gas-poor magma was squeezed into a developing ring-fault system by the subsiding chamber roof. Spatial heterogeneities in ascent rates and outgassing through this variably dilated fault system caused coeval formation of collapsing plumes and spatter fountains at separate vents. Spatter was entrained into flows from the more explosive vents, which deposited proximal spatter agglomerates and more distal spatter-bearing ignimbrite. Overlying lava-like ignimbrite deposits (basaltic andesite to basalt) reflect a final opening of vents, as mafic magma from deep levels of the chamber was squeezed through a dilated ring-fault system by the subsiding roof block and erupted at uncharacteristically high mass flux. Development of a mature ring-fault conduit system during early tapping of silicic magma appears to be a prerequisite for the emplacement of welded basaltic ignimbrites, and it should be considered as a possible eruption scenario in basalt-dominated systems where silicic magma has been known to also accumulate. Poor preservation of the Halarauður deposits exemplifies the challenges of studying ignimbrite eruptions in frequently glaciated regions like Iceland, where they may be more common than the geological record suggests.
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Varga, Robert J., Roy A. Bailey, and Gene A. Suemnicht. "Evidence for 600 year-old basalt and magma mixing at Inyo Craters Volcanic Chain, Long Valley Caldera, California." Journal of Geophysical Research 95, B13 (1990): 21441. http://dx.doi.org/10.1029/jb095ib13p21441.
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BRYAN, S. E., J. MARTÍ, and R. A. F. CAS. "Stratigraphy of the Bandas del Sur Formation: an extracaldera record of Quaternary phonolitic explosive eruptions from the Las Cañadas edifice, Tenerife (Canary Islands)." Geological Magazine 135, no. 5 (September 1998): 605–36. http://dx.doi.org/10.1017/s0016756897001258.
Повний текст джерелаАнотація:
Explosive volcanism has dominated the large phonolitic shield volcano of Tenerife, the Las Cañadas edifice, for the last 1.5 m.y. Pyroclastic deposits of the Bandas del Sur Formation are exposed along the southern flanks, and record the last two of at least three long-term cycles of caldera-forming explosive eruptions. Each cycle began with flank fissure eruptions of alkali basalt lava, followed by minor eruptions of basanite to phonotephrite lavas. Minor phonotephritic to phonolitic lava effusions also occurred on the flanks of the edifice during the latter stages of the second explosive cycle. Non-welded plinian fall deposits and ignimbrites are the dominant explosive products preserved on the southern flanks. Of these, a significant volume has been dispersed offshore. Many pyroclastic units of the second explosive cycle exhibit compositional zonation. Banded pumice occurs in most units of the third (youngest) explosive cycle, and ignimbrites typically contain mixed phenocryst assemblages, indicating the role of magma mixing/mingling prior to eruption. At least four major eruptions of the third cycle began with phreatomagmatic activity, producing lithic-poor, accretionary lapilli-bearing fallout and/or surge deposits. The repeated, brief phase of phreatomagmatism at the onset of these eruptions is interpreted as reflecting an exhaustive water supply, probably a small caldera lake that was periodically established during the third cycle. Accidental syenite becomes an increasingly important lithic clast type in ignimbrites up-sequence, and is interpreted as recording the progressive development of a plutonic complex beneath the summit caldera.Successive eruptions during each explosive cycle increased in volume, with the largest eruption occurring at the end of the cycle. More than ten major explosive eruptions vented moderately large volumes (1−[ges ]10 km3) of phonolitic magma during the last two cycles. Culminating each explosive cycle was the emplacement of relatively large volume (>5−10 km3) ignimbrites with coarse, vent-derived lithic breccias, interpreted to record a major phase of caldera collapse. In the extracaldera record, explosive cycles are separated by ∼0.2 m.y. periods of non-explosive activity. Repose periods were characterized by erosion, remobilization of pyroclastic deposits by discharge events, and pedogenesis. The current period of non-explosive activity is characterized by the construction of the Teide-Pico Viejo stratovolcanic complex within the summit caldera. This suggests that eruptive hiatuses in the extracaldera record may reflect effusive activity and stratovolcano or shield-building phases within the summit caldera. Alternating effusive and explosive cycles have thus been important in the volcanic evolution of the Las Cañadas edifice.
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Smirnov, S. Z., A. V. Rybin, N. N. Kruk, T. Yu Timina, E. N. Sokolova, D. V. Kuzmin, I. A. Maksimovich, et al. "Parental Melts and Magma Storage of a Large-volume Dacite Eruption at Vetrovoy Isthmus (Iturup Island, Southern Kuril Islands): Insights into the Genesis of Subduction-zone Dacites." Journal of Petrology 60, no. 7 (June 13, 2019): 1349–70. http://dx.doi.org/10.1093/petrology/egz032.
Повний текст джерелаАнотація:
Abstract Detailed mineralogical and melt and fluid inclusion constraints on magma storage, and the evolution of melts, are presented for the large-volume caldera eruption on the Vetrovoy Isthmus on Itutrup Island (Kuril Islands, Russia). The shallow magma reservoir beneath the Vetrovoy Isthmus is composed of a mush of plagio-rhyolitic melt, phenocrysts and the products of peritectic reaction(s). The melt appears to have formed as a result of partial melting of previously erupted rocks, which probably had andesitic to basaltic compositions and were metamorphosed into amphibole-bearing assemblages. The breakdown of amphibole in the partially melted precursor rocks led to the formation of early Mg-rich clino- and orthopyroxene, along with plagioclase and Fe–Ti oxides, and the release of aqueous fluids. Variations in fluid pressure are recorded by a strong increase of An contents in plagioclase. Crystallization took place at around 850°C with pressure ranging from 0·9 to 3 kbar. This study demonstrates that dacitic magmas erupted during the course of a 20 kyr voluminous eruption were the result of mixing between plagio-rhyolitic partial melts and the breakdown reaction minerals (i.e. pyroxenes, plagioclase and Fe–Ti oxides). Plagioclase and quartz were the last minerals to crystallize from these melts prior to eruption.
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Shcherbakov, Vasily, Ilya Bindeman, and Viktor Gazeev. "Geochemical, Isotopic and Petrological Constraints on the Origin and Evolution of the Recent Silicic Magmatism of the Greater Caucasus." Minerals 12, no. 1 (January 16, 2022): 105. http://dx.doi.org/10.3390/min12010105.
Повний текст джерелаАнотація:
Significant volumes of rhyolites and granites of the Pliocene-Pleistocene age are exposed in the collision zone of the Greater Caucasus, Russia. The volcanic history of the region includes ignimbrites and lavas associated with the Chegem caldera (2.9 Ma) and Elbrus volcano (1.98 and 0.7 Ma) and rhyolitic necks and granites in Tyrnyauz (1.98 Ma). They are characterized by a similar bulk and mineral composition and close ratios of incompatible elements, which indicates their related origin. The 1.98 Ma Elbrus ignimbrites, compared to the 2.9 Ma Chegem ignimbrites, have elevated concentrations of both compatible (Cr, Sr, Ca, Ni) and incompatible elements (Cs, Rb, U). We argue that the Elbrus ignimbrites were produced from magma geochemically similar to Chegem rhyolites through fractionation crystallization coupled with the assimilation of crustal material. The 1.98 Ma Eldjuta granites of Tyrnyauz and early ignimbrites of the Elbrus region (1.98 Ma) are temporally coeval, similar mineralogically, and have comparable major and trace element composition, which indicates that the Elbrus ignimbrites probably erupted from the area of modern Tyrnyauz; the Eldjurta granite could represent a plutonic reservoir that fed this eruption. Late ignimbrites of Elbrus (0.7 Ma) and subsequent lavas demonstrate progressively more mafic mineral assemblage and bulk rock composition in comparison with rhyolites. This indicates their origin in response to the mixing of rhyolites with magmas of a more basic composition at the late stage of magma system development. The composition of these basic magmas may be close to the basaltic trachyandesite, the flows exposed along the periphery of the Elbrus volcano. All studied young volcanic rocks of the Greater Caucasus are characterized by depletion in HSFE and enrichment in LILE, Li, and Pb, which emphasizes the close relationship of young silicic magmatism with magmas of suprasubduction geochemical affinity. An important geochemical feature is the enrichment of U up to 8 ppm and Th up to 35 ppm. The trace element composition of the rocks indicates that the original rhyolitic magma of Chegem ignimbrites caldera was formed at >80%–90% fractionation of calc-alkaline arc basalts with increased alkalinity. This observation, in addition to published data for isotopic composition (O-Hf-Sr) of the same units, shows that the crustal isotopic signatures of silicic volcanics may arise due to the subduction-induced fertilization of peridotites producing parental basaltic magmas before a delamination episode reactivated the melting of the former mantle and the lower crust.
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Carrasco-Nunez, G., M. McCurry, M. J. Branney, M. Norry, and C. Willcox. "Complex magma mixing, mingling, and withdrawal associated with an intra-Plinian ignimbrite eruption at a large silicic caldera volcano: Los Humeros of central Mexico." Geological Society of America Bulletin 124, no. 11-12 (September 14, 2012): 1793–809. http://dx.doi.org/10.1130/b30501.1.
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Hernando, Irene Raquel, Ivan Alejandro Petrinovic, Eduardo Jorge Llambías, Leandro D'Elia, Pablo Diego González, and Eugenio Aragón. "The role of magma mixing and mafic recharge in the evolution of a back-arc quaternary caldera: The case of Payún Matrú, Western Argentina." Journal of Volcanology and Geothermal Research 311 (February 2016): 150–69. http://dx.doi.org/10.1016/j.jvolgeores.2016.01.008.
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Stelten, Mark E., Kari M. Cooper, Jorge A. Vazquez, Mary R. Reid, Gry H. Barfod, Josh Wimpenny, and Qing-zhu Yin. "Magma mixing and the generation of isotopically juvenile silicic magma at Yellowstone caldera inferred from coupling 238U–230Th ages with trace elements and Hf and O isotopes in zircon and Pb isotopes in sanidine." Contributions to Mineralogy and Petrology 166, no. 2 (June 27, 2013): 587–613. http://dx.doi.org/10.1007/s00410-013-0893-2.
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Swallow, Elliot J., Colin J. N. Wilson, Bruce L. A. Charlier, and John A. Gamble. "The Huckleberry Ridge Tuff, Yellowstone: evacuation of multiple magmatic systems in a complex episodic eruption." Journal of Petrology 60, no. 7 (June 28, 2019): 1371–426. http://dx.doi.org/10.1093/petrology/egz034.
Повний текст джерелаАнотація:
Abstract The 2·08 Ma, ∼2500 km3 Huckleberry Ridge Tuff (HRT) eruption, Yellowstone, generated two fall deposits and three ignimbrite members (A, B, C), accompanying a ∼95 x 65 km caldera collapse. Field data imply that the pre-A fall deposits took weeks to be erupted, then breaks of weeks to months occurred between members A and B, and years to decades between B and C. We present compositional and isotopic data from single silicic clasts (pumice or fiamme) in the three ignimbrite members, plus new data from co-eruptive mafic components to reconstruct the nature and evacuation history of the HRT crustal magmatic complex. Geochemical data, building on field characteristics, are used to group nine silicic clast types into seven compositional suites (A1-A3; B1; C1-C3) within their respective members A, B and C. Isotopic data are then added to define four magmatic systems that were tapped simultaneously and/or sequentially during the eruption. Systems 1 and 2 fed the initial fall deposits and then vented throughout member A, accompanied by trace amounts of mafic magma. In member A, volumetrically dominant system 1 is represented by a rhyolite suite (A1: 73·0–77·7 wt % SiO2, 450–1680 ppm Ba) plus a distinct low-silica rhyolite suite (A2: 69·2–71·6 wt % SiO2, >2500 ppm Ba). System 2 yielded only a low-Ba, high-silica rhyolite suite (A3: 76·7–77·4 wt % SiO2, ≤250 ppm Ba). Glass compositions in pumices from systems 1 and 2 show clustering, indicative of the same multiple melt-dominant bodies identified in the initial fall deposits and earliest ignimbrite. Member B samples define suite B1 (70·7–77·4 wt % SiO2, 540–3040 ppm Ba) derived from magmatic system 1 (but not 2) that had undergone mixing and reorganisation during the A: B time break, accompanying mafic magma inputs. Mafic scoriae erupted in upper member B cover similar compositions to the member A clasts, but extend over a much broader compositional range. Member C clast compositions reflect major changes during the B: C time break, including rejuvenation of magmatic system 2 (last seen in member A) as suite C3 (75·3–77·2 wt % SiO2, 100–410 ppm Ba), plus the appearance of two new suites with strong crustal signatures. Suite C2 is another rhyolite (74·7–77·6 wt % SiO2, with Ba decreasing with silica from 2840 to 470 ppm) that defines magmatic system 3. Suite C2 also shows clustered glass compositions, suggesting that multiple melt-dominant bodies were a repetitive feature of the HRT magmatic complex. Suite C1, in contrast, is dacite to rhyolite (65·6–75·0 wt % SiO2, with Ba increasing with silica from 750 to 1710 ppm) that defines magmatic system 4. Compositions from magmatic systems 1 and 2 dominantly reflect fractional crystallization, but include partial melting of cumulates related to earlier intrusions of the same mafic magmas as those syn-eruptively vented. Country rock assimilation was limited to minor amounts of a more radiogenic (with respect to Sr) evolved contaminant. In contrast, systems 3 and 4 show similar strongly crustal isotopic compositions (despite their differences in elemental composition) consistent with assimilation of Archean rocks via partial melts derived from cumulates associated with contrasting mafic lineages. System 3 links to the same HRT mafic compositions co-erupted in members A and B. In contrast, system 4 links to olivine tholeiite compositions erupted in the Yellowstone area before, sparsely during, and following the HRT itself. All four magmatic systems were housed beneath the HRT caldera area. Systems 1 and 2 were hosted in Archean crust that had been modified by Cretaceous/Eocene magmatism, whereas systems 3 and 4 were hosted within crust that retained Archean isotopic characteristics. The extreme compositional diversity in the HRT highlights the spatial and temporal complexities that can be associated with large-volume silicic magmatism.
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Ewart, A., R. W. Schon, and B. W. Chappell. "The Cretaceous volcanic-plutonic province of the central Queensland (Australia) coast—a rift related ‘calc-alkaline’ province." Earth and Environmental Science Transactions of the Royal Society of Edinburgh 83, no. 1-2 (1992): 327–45. http://dx.doi.org/10.1017/s0263593300008002.
Повний текст джерелаАнотація:
ABSTRACTSilicic and minor intermediate and mafic pyroclastics, lavas, and dykes occupy a NW-trending zone through the Whitsunday, Cumberland and Northumberland Island groups, and locally areas on the adjacent mainland, over a distance of more than 300 km along the central Queensland coast. K-Ar and Rb-Sr data indicate an age range of 95–132 Ma, with the main activity approximately between 105–120 Ma; there is, however, evidence for easterly increasing ages. Comagmatic granites, some clearly intrusive into the volcanics, occur together with two localised areas of Triassic potassic granites (229 Ma), that form the immediate basement.The volcanics are dominantly rhyolitic to dacitic lithic ignimbrites, with intercalated surge and bedded tuffs, accretionary lapilli tuffs, and lag deposits. Associated rock types include isolated rhyolitic and dacitic domes, and volumetrically minor andesite and rare basalt flows. The sequence is cut by abundant dykes, especially in the northern region and adjacent mainland, ranging from dolerite through andesite, dacite and rhyolite. Dyke orientations show maxima between NW-NNE. Isotope data, similarities in petrography and mineralogy, and alteration patterns all suggest dyke intrusion to be broadly contemporaneous with volcanism. The thickness of the volcanics is unconstrained, although in the Whitsunday area, minimum thicknesses of >1 km are inferred. Eruptive centres are believed to occur throughout the region, and include at least two areas of caldera-style collapse. The sequences are thus considered as predominantly intracaldera.The phenocryst mineralogy is similar to modern “orogenic” volcanics. Phases include plagioclase, augite, hypersthene (uralitised), magnetite, ilmenite, with less common hornblende, and even rarer quartz, sanidine, and biotite. Fe-enriched compositions only develop in some high-silica rhyolites. The granites range from quartz diorite to granite s.s., and some contain spectacular concentrations of partially disaggregated dioritic inclusions.Chemically, the suite ranges continuously from basalt to high-silica rhyolite, with calc-alkali to high-K affinities, and geochemical signatures similar to modern subduction-related magmas. Only the high-silica rhyolites and granites exhibit evidence of extensive fractional crystallisation (e.g. pronounced Eu anomalies). Variation within the suite can only satisfactorily be modelled in terms of two component mixing, with superimposed crystal fractionation. Nd and Sr isotope compositions are relatively coherent, with εNd + 2·2 to +7·3, and ISr (calculated at 110 and 115 Ma) 0·7031-0·7044. These are relatively primitive, and imply mantle and/or newly accreted crustal magma sources.The two end-members proposed are within-plate tholeiitic melt, and ?low-silica rhyolitic melts generated by partial fusion of Permian (to ?Carboniferous) arc and arc basement. The arc-like geochemistry is thus considered to be source inherited. The tectonic setting for Cretaceous volcanism is correlated with updoming and basin rifting during the early stages of continental breakup, culminating in the opening of the Tasman Basin. Cretaceous volcanism is also recognised in the Maryborough Basin (S Queensland), the Lord Howe Rise, and New Caledonia, indicating the regional extent of volcanism associated with the complex breakup of the eastern Australasian continent margin.
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Bernard, Olivier, Weiran Li, Fidel Costa, Steve Saunders, Ima Itikarai, Mikhail Sindang, and Caroline Bouvet de Maisonneuve. "Explosive-effusive-explosive: The role of magma ascent rates and paths in modulating caldera eruptions." Geology, May 27, 2022. http://dx.doi.org/10.1130/g50023.1.
Повний текст джерелаАнотація:
One of the biggest challenges in volcanology is assessing the role of magma properties (volatile budgets, storage depths, and ascent rates) in controlling eruption explosivity. We use a new approach based on apatite to estimate volatile contents and magma ascent rates from a sequence of sub-Plinian, effusive, and Vulcanian eruption deposits at Rabaul caldera (Papua New Guinea) emplaced in 2006 CE to probe the mechanisms responsible for the sudden transitions in eruption styles. Our findings show that all magmas were originally stored at similar conditions (2–4 km depth and 1.8–2.5 wt% H2O in the melt); only the magma that formed the lava flow stalled and degassed at a shallower level (0.2–1.5 km) for several months. A more energetic batch of magma rose from depth, bypassed the transient reservoir, and ascended within ≤8 h to Earth’s surface (mean velocity ≥0.2 m/s), yielding the initial sub-Plinian phase of the eruption. The shallowly degassed magma was then able to reach the surface as a lava flow, likely through the path opened by the sub-Plinian magma. The magma of the last Vulcanian phase ascended without storage at a shallow depth, albeit more slowly (ascent rate 0.03–0.1 m/s) than the sub-Plinian magma. Our study illustrates how the complexity of plumbing systems may affect eruption styles, including at other volcanic systems, and have implications for interpreting volcano monitoring data.
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Gilmer, Amy K., Ren A. Thompson, Peter W. Lipman, Jorge A. Vazquez, and A. Kate Souders. "Postcaldera intrusive magmatism at the Platoro caldera complex, Southern Rocky Mountain volcanic field, Colorado, USA." Geosphere, April 2, 2021. http://dx.doi.org/10.1130/ges02242.1.
Повний текст джерелаАнотація:
The Oligocene Platoro caldera complex of the San Juan volcanic locus in Colorado (USA) features numerous exposed plutons both within the caldera and outside its margins, enabling investigation of the timing and evolution of postcaldera magmatism. Intrusion whole-rock geochemistry and phenocryst and/or mineral trace element compositions coupled with new zircon U-Pb geochronology and zircon in situ Lu-Hf isotopes document distinct pulses of magma from beneath the caldera complex. Fourteen intrusions, the Chiquito Peak Tuff, and the dacite of Fisher Gulch were dated, showing intrusive magmatism began after the 28.8 Ma eruption of the Chiquito Peak Tuff and continued to 24 Ma. Additionally, magmatic-hydrothermal mineralization is associated with the intrusive magmatism within and around the margins of the Platoro caldera complex. After caldera collapse, three plutons were emplaced within the subsided block between ca. 28.8 and 28.6 Ma. These have broadly similar modal mineralogy and whole-rock geochemistry. Despite close temporal relations between the tuff and the intrusions, mineral textures and compositions indicate that the larger two intracaldera intrusions are discrete later pulses of magma. Intrusions outside the caldera are younger, ca. 28–26.3 Ma, and smaller in exposed area. They contain abundant glomerocrysts and show evidence of open-system processes such as magma mixing and crystal entrainment. The protracted magmatic history at the Platoro caldera complex documents the diversity of the multiple discrete magma pulses needed to generate large composite volcanic fields.
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González-García, Diego, Maurizio Petrelli, Diego Perugini, Daniele Giordano, Jérémie Vasseur, Joali Paredes-Mariño, Joan Marti, and Donald B. Dingwell. "Pre-Eruptive Conditions and Dynamics Recorded in Banded Pumices from the El Abrigo Caldera-Forming Eruption (Tenerife, Canary Islands)." Journal of Petrology 63, no. 3 (February 15, 2022). http://dx.doi.org/10.1093/petrology/egac009.
Повний текст джерелаАнотація:
Abstract The El Abrigo member of the Diego Hernández Formation (Tenerife, Canary Islands) represents the final (170 ka) and most voluminous eruption (>20-km3 DRE) of the last cycle of explosive activity of the Las Cañadas volcano. It is a dominantly phonolitic ignimbrite containing both mafic and banded pumices, suggesting that magma mixing played an important role in triggering the eruption and modulating eruptive dynamics. Here we use petrology, together with glass and mineral geochemistry of enclave-rich mafic scoriae, banded and phonolitic pumices from El Abrigo ignimbrite, to shed light on the pre-eruptive storage conditions and processes governing magma ascent and interaction dynamics and to provide a first-order assessment of the contribution of magma mixing and crystal mush melting to the dynamics of this eruptive event. The distribution of major elements in glasses is consistent with diffusive exchange between the interacting melts whereby Na transfers from the phonolite to the tephriphonolitic melt. However, V, Zr, Ba, and Eu suggest a complex scenario in which an intruding tephritic to phonotephritic magma interacted with two distinct zones of a phonolitic magma chamber, one occupied by a crystal-rich, low-Zr, and high-Ba phonolite, and the other by an evolved, crystal-poor, high-Zr phonolite. These results, coupled with mineral–melt thermobarometry, allow us to reconstruct the Las Cañadas plumbing system at the end of the Diego Hernández cycle and to evaluate the contribution of cumulate mush melting and magma mixing in as follows: (1) the parental tephritic magma was stored at or near the Moho (410–450 MPa) at 1050°C where it was periodically replenished by more primitive basanitic magma; (2) upon ascent, the tephrite intruded into a shallow and zoned phonolitic storage system, triggering the disruption of a crystal mush in its base; and (3) subsequently interacted with a crystal-poor zone within the reservoir. Energy balance evaluations suggest that relative mafic magma volume ratios ranged from 20 to 43 vol%, and the conservation of small-scale magma mingling structures and their geochemical distribution suggest that the mixing event took place very shortly before the eruption, on a timescale of hours.
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Wu, Jie, Michael C. Rowe, Shane J. Cronin, and John A. Wolff. "Mineralogical Evidence of Pre-caldera Magma Petrogenesis in the Jemez Mountains Volcanic Field, New Mexico, USA." Journal of Petrology 61, no. 7 (June 22, 2020). http://dx.doi.org/10.1093/petrology/egaa064.
Повний текст джерелаАнотація:
Abstract The Jemez Mountains volcanic field (JMVF) is the site of the two voluminous, caldera-forming members of the Bandelier Tuff, erupted at 1·60 and 1·25 Ma, following a long and continuous pre-caldera volcanic history (∼10 Myr) in this region. Previous investigations utilizing whole-rock geochemistry identified complex magmatic processes in the two major pulses of pre-caldera magmatism including assimilation–fractional crystallization (AFC) and magma mixing. Here we extend the petrological investigation of the pre-caldera volcanic rocks into the micro-realm and use mineral chemistry and textural information to refine magma evolution models. The results show an increasing diversity of mineral populations as the volcanic field evolved. A range of plagioclase textures (e.g. sieved cores and rims) indicate disequilibrium conditions in almost all pre-caldera magmas ranging from andesite to rhyolite, reflecting plagioclase dissolution and regrowth. Coarsely sieved or dissolved plagioclase cores are explained by resorption via water-undersaturated decompression during upward migration from a deep melting, assimilation, storage and homogenization (MASH) zone. Plagioclase crystals with sieved rims are almost ubiquitous in dacite-dominated magmatism (La Grulla Plateau andesite and dacite erupted at ∼8–7 Ma, as well as Tschicoma Formation andesite, dacite and rhyolite at ∼5–2 Ma), reflecting heating induced by magma mixing. These plagioclase crystals often have An-poor cores that are chemically distinct from their An-rich rims. The existence of different plagioclase populations is consistent with two distinct amphibole groups that co-crystallized with plagioclase: a low-Al, low-temperature, high-fO2 group, and a high-Al, high-temperature, low-fO2 group. Calculation of melt Sr, Ba, La, and Ce concentrations from plagioclase core and rim compositions suggests that these chemical variations are largely produced by magma mixing. Multiple mafic endmembers were identified that may be connected by AFC processes in the MASH zone in the middle to lower crust. The silicic component in an early andesite-dominated magmatic system (Paliza Canyon andesite, dacite and rhyolite, 10–7 Ma) is represented by contemporaneous early rhyolite (Canovas Canyon Rhyolite). A silicic mush zone in the shallow crust is inferred as both the silicic endmember involved in the dacite-dominant magmatic systems and source of the late low-temperature rhyolite (Bearhead Rhyolite, 7–6 Ma). Recharging of the silicic mush by mafic melts can explain observed diversity in both mineral disequilibrium textures and compositions in the dacitic magmas. Overall, the pre-caldera JMVF magmatic system evolved towards cooler and more oxidized conditions with time, indicating gradual thermal maturation of local crust, building up to a transcrustal magmatic system, which culminated in ‘super-scale’ silicic volcanism. Such conditioning of crust with heat and mass by early magmatism might be common in other long-lived volcanic fields.
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Curry, Adam, Luca Caricchi, and Peter W. Lipman. "Magmatic Evolution of Zoned and Unzoned Ignimbrites: Evidence for a Complex Crustal Architecture Feeding four Rapid-sequence, Caldera-forming Eruptions in the San Juan Mountains, Colorado." Journal of Petrology 62, no. 5 (January 28, 2021). http://dx.doi.org/10.1093/petrology/egab006.
Повний текст джерелаАнотація:
Abstract The last four caldera-forming ignimbrites in the central San Juan caldera cluster, Colorado, erupted 1400 km3 in ≤80 kyr and alternated between zoned crystal-poor rhyolite to crystal-rich dacite and unzoned, crystal-rich dacite. The zoned 150 km3 Rat Creek Tuff (26·91 Ma), unzoned 250 km3 Cebolla Creek Tuff, and zoned 500 km3 Nelson Mountain Tuff (26·90 Ma) formed the nested San Luis caldera complex with slightly offset calderas, and the unzoned 500 km3 Snowshoe Mountain Tuff (26·87 Ma) formed the Creede caldera to the south. The Rat Creek Tuff, Nelson Mountain Tuff, and Snowshoe Mountain Tuff have similar mineral assemblages of plagioclase, sanidine, quartz, biotite, hornblende, clinopyroxene, Fe–Ti oxides, and accessory zircon, titanite, and apatite. The Cebolla Creek Tuff differs from the other three ignimbrites with more abundant hornblende and a lack of quartz and sanidine. Trace element compositions of interstitial glass are unique to each ignimbrite, correlating with mineral assemblages and inferred crystallization depths. Glass, feldspar, hornblende, and clinopyroxene thermobarometry calculations provide evidence for vertically extensive crustal magma reservoirs with a common magmatic zone at ∼435–470 MPa (∼16–17 km) showing a transition into shallow pre-eruptive reservoirs between ∼110 and 340 MPa (∼4–13 km), similar to the estimated magma reservoir architecture of the Altiplano Puna Volcanic Complex. The upper portions of the eruptible parts of the magma reservoirs of the Rat Creek Tuff (215 ± 50 MPa, ∼810–820 °C), Cebolla Creek Tuff (340 ± 20 MPa, ∼860–880 °C), Nelson Mountain Tuff (215 ± 20 MPa, ∼745–800 °C), and Snowshoe Mountain Tuff (110 ± 40 MPa, 825 ± 10 °C) occupied shallow levels in the crust similar to other magma reservoirs of the central San Juan caldera cluster. Trace element modelling correlates with a deep crystallization signature in the unzoned Cebolla Creek Tuff and Snowshoe Mountain Tuff, typified by a flat trend in Ba versus Sr whole-rock and glass chemistry. The zoned Rat Creek Tuff and Nelson Mountain Tuff are typified by a steep trend in Ba versus Sr chemistry interpreted as a shallower crystallization signature. Similarly, the unzoned Cebolla Creek Tuff and Snowshoe Mountain Tuff have flatter slopes in FeO versus An space of plagioclase chemistry interpreted as more abundant deep plagioclase crystallization and a difficulty in physically mixing with Fe-rich mafic recharge magma owing to higher viscosity. The zoned Rat Creek Tuff and Nelson Mountain Tuff have higher slopes in FeO versus An space of plagioclase chemistry interpreted as more abundant shallow plagioclase crystallization and more feasible mixing with Fe-rich mafic recharge magma owing to lower viscosity. The eruption of the Rat Creek Tuff was probably triggered by mafic injection, but the other three ignimbrites lack mingling textures in pumice, suggesting that other mechanisms were important in causing such large eruptions. After a prolonged period of mantle-derived magma injection and crustal heating (∼25 000 km3 Conejos Formation erupted during ∼35–29 Ma), the San Juan magmatic body became a robust and versatile producer of diverse eruptible magmas in short time periods during its Oligocene ignimbrite flare-up.
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Geshi, Nobuo, Teruki Oikawa, Derek J. Weller, and Chris E. Conway. "Evolution of the magma plumbing system of Miyakejima volcano with periodic recharge of basaltic magmas." Earth, Planets and Space 74, no. 1 (January 29, 2022). http://dx.doi.org/10.1186/s40623-022-01577-7.
Повний текст джерелаАнотація:
AbstractDefining the variations in petrological characteristics of erupted magmas within a high-resolution chronostratigraphy provides a necessary framework for monitoring the long-term activity and eruption potential of an active volcano. Here, we investigate the evolution of the magmatic system of Miyakejima volcano, Japan, between the last two caldera-forming eruptions, at ~ 2.3 ka and AD 2000, based on new stratigraphic constraints, radiocarbon ages, and whole-rock geochemical data. The activity of Miyakejima during this interval can be divided into three magmatic periods based on cyclic whole-rock compositional trends. Period 1 spans the interval between ~ 2.3 ka and the 7th century, from the Hatchodaira eruption with caldera collapse to immediately before the Suoana–Kazahaya eruption. Period 2 spans the time period between the seventh century and the fourteenth century, from the Suoana–Kazahaya to the Sonei–bokujyo eruptions. Period 3 covers the period from the two major flank eruptions that occurred in the sixteenth century to the end of the twentieth century until the last caldera-collapse event in AD 2000. The eruption rate decreased from 0.5 km3 per 1000 years in Period 1 to ~ 0.2 km3 per 1000 years in Period 2 and 3. Recharge of primitive basaltic magmas into shallower crustal systems triggered extensive basaltic fissure eruptions at the beginning of each period. Progressively increasing whole-rock SiO2 contents of the hybrid magmas in subsequent eruptions indicates continuous fractional crystallization in small shallow magma chambers which formed at the start of each magmatic period. Intermittent injections of basaltic magma into shallow magma chambers induced magma mixing that caused eruption of hybrid basaltic andesite in each period. We suggest that some basaltic magmas formed isolated magma reservoirs at shallow depth, in which rapid fractionation was able to occur. Rupturing of these isolated magma storage regions filled with gas-rich evolved magma can lead to violent ejection of andesitic magmas, such as for the Suoana–Kazahaya eruption in the seventh century. Our results suggest two main scenarios of eruption for the basaltic magma system at Miyakejima and similar mafic volcanoes in the northern Izu–Bonin arc; (1) eruption of voluminous basaltic lavas after the recharge of primitive basaltic magmas into the shallow magmatic system, and (2) explosive fissure eruption by rupturing of isolated magma bodies filled with gas-rich evolved magmas. Graphical Abstract
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Gavrilenko, Maxim, Alexey Ozerov, Philip R. Kyle, Michael J. Carr, Alex Nikulin, Christopher Vidito, and Leonid Danyushevsky. "Abrupt transition from fractional crystallization to magma mixing at Gorely volcano (Kamchatka) after caldera collapse." Bulletin of Volcanology 78, no. 7 (June 7, 2016). http://dx.doi.org/10.1007/s00445-016-1038-z.
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Pamukçu, Ayla S., Blair Schoene, Chad D. Deering, C. Brenhin Keller, and Michael P. Eddy. "Volcano-pluton connections at the Lake City magmatic center (Colorado, USA)." Geosphere, August 11, 2022. http://dx.doi.org/10.1130/ges02467.1.
Повний текст джерелаАнотація:
Exposed at the Lake City caldera (Colorado, USA) is the ca. 23 Ma reversely stratified (rhyolite to trachyte) Sunshine Peak Tuff and post-collapse syenite and monzonite resurgent intrusions. Existing models for this system suggest that the rhyolites are related to the trachyte and resurgent syenite through fractional crystallization, separation, and remobilization (crystal mush model), and that multiple magma batches were involved in the system (Hon, 1987; Kennedy et al., 2016; Lubbers et al., 2020). We use U-Pb zircon CA-ID-TIMS-TEA and zircon trace-element modeling to further probe age and geochemical relationships between the extrusive and intrusive units. Zircon ages and compositions from the erupted units and the syenite overlap, suggesting these magmas were related and may have mixed prior to eruption. Results from the monzonite suggest it was a contemporaneous but distinct magma batch that mixed with parts of the larger system. Trends in zircon geochemistry are decoupled from time, reflecting a complex history of accessory mineral saturation and mixing of magma batches, and a distinct high-Hf population of zircon grains hints at the existence of an additional, independent batch of rhyolitic magma in the system. The new ages we present shorten the lifetime of the Lake City magmatic system from 80 to 300 k.y. (Bove et al., 2001) to 60 to 220 k.y. and suggest the high-silica rhyolite magma crystallized over a minimum of ~160 k.y. This latter timescale likely reflects a protracted history that includes differentiation of a parent melt prior to extraction of eruptible high-silica rhyolite magma.
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Sas, May, Phil Shane, Takeshi Kuritani, Georg F. Zellmer, Adam J. R. Kent, and Mitsuhiro Nakagawa. "Mush, melts and metasediments: A history of rhyolites from the Okataina Volcanic Centre, New Zealand, as captured in plagioclase." Journal of Petrology, May 1, 2021. http://dx.doi.org/10.1093/petrology/egab038.
Повний текст джерелаАнотація:
Abstract The Okataina Volcanic Centre (OVC), located in the Taupo Volcanic Zone, New Zealand, is a dominantly rhyolitic magmatic system in an arc setting, where eruptions are thought to be driven by mafic recharge. Here, Sr-Pb isotopes, and compositional and textural variations in plagioclase phenocrysts from ten rhyolitic deposits (two caldera, one immediately post-caldera, four intra-caldera, and three extra-caldera) are used to investigate the OVC magmatic system and identify the sources and assimilants within this diverse mush zone. Plagioclase interiors exhibit normal and reverse zoning, and are commonly in disequilibrium with their accompanying glass, melt inclusions, and whole rock compositions. This indicates that the crystals nucleated in melts that differed from their carrier magma. In contrast, the outermost rims of crystals exhibit normal zoning that is compositionally consistent with growth in cooling and fractionating melts just prior to eruption. At the intra-crystal-scale, the total suite of 87Sr/86Sr ratios are highly variable (0.7042–0.7065 ± 0.0004 average 2se), however, the majority (95%) of the crystals are internally homogeneous within error. At whole-crystal-scale (where better precision is obtained) 87Sr/86Sr ratios are much more homogeneous (0.70512–0.70543 ± 0.00001 average 2se) and overlap with their host whole rock Sr isotopic ratios. Whole-crystal Pb isotopic ratios also largely overlap with whole rock Pb ratios. The plagioclase and whole rock isotopic compositions indicate significant crustal assimilation (≥20%) of Torlesse-like metasediments (local basement rock) by a depleted mid-ocean ridge mantle magma source, and Pb isotopes require variable fluid-dominant subduction flux. The new data support previous petrogenetic models for OVC magmas that require crystal growth in compositionally and thermally distinct magmas within a complex of disconnected melt-and-mush reservoirs. These reservoirs were rejuvenated by underplating basaltic magmas that serve as an eruption trigger. However, the outermost rims of the plagioclase imply interaction between silicic melts and eruption-triggering mafic influx is largely limited to heat and volatile transfer, and results in rapid mobilization and syn-eruption mixing of rhyolitic melts. Finally, relatively uniform isotopic compositions of plagioclase indicate balanced contributions from the crust and mantle over the lifespan of the OVC magmatic system.
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Keller, Franziska, Olivier Bachmann, Nobuo Geshi, and Ayumu Miyakawa. "The Role of Crystal Accumulation and Cumulate Remobilization in the Formation of Large Zoned Ignimbrites: Insights From the Aso-4 Caldera-forming Eruption, Kyushu, Japan." Frontiers in Earth Science 8 (February 26, 2021). http://dx.doi.org/10.3389/feart.2020.614267.
Повний текст джерелаАнотація:
The Aso-4 caldera-forming event (86.4 ± 1.1 ka, VEI-8) is the second largest volcanic eruption Earth experienced in the past 100 ka. The ignimbrite sheets produced during this event are some of the first ever described compositionally zoned pyroclastic flow deposits exhibiting clear compositional, mineralogical and thermal gradients with stratigraphic position. Large quantities of the deposits are composed of crystal-poor, highly evolved juvenile pumices, while late-erupted pyroclastic flows are in many cases dominated by crystal-rich and less silicic scoria. These petrological gradients in the Aso-4 deposits have been linked to extensive magma mixing of two compositionally distinct magmas in a complex upper crustal reservoir. However, new studies on several other zoned ignimbrites suggest that magma mixing alone is not sufficient to fully explain such strong compositional gradients in the deposits. These gradients are expected to be dominantly caused by the recharge-induced reactivation of extracted melt caps and their complementary cumulate in the upper crust. Here, we investigate bulk rock and matrix glass data with detailed analyses of mineral chemistry in order to re-evaluate the Aso-4 deposits in light of these latest developments. Reverse chemical zoning in phenocrysts, Sr enrichment in euhedral rims of plagioclase and the presence of mafic minerals (clinopyroxene, olivine) indicate recharge of hot, mafic magmas shortly prior to eruption, inducing a mixing signature. However, the marked enrichment in some elements in bulk-rock analyses and the presence of highly evolved minerals (some in the form of glomerocrysts) in the late-erupted, crystal-rich units, provide clear evidence for crystal accumulation in these scoria. Mass balance modeling of P2O5, Sr and SiO2 supports the extraction of melt-rich lenses within an upper crustal mush zone, leaving a partly cumulative evolved crystal residue. We therefore propose an origin of the compositionally zoned Aso-4 ignimbrite largely by erupting a heterogeneous upper crustal reservoir, consisting of crystal-poor rhyodacitic melt caps within its associated cumulate mush. This complex reservoir was reactivated by mafic recharge shortly prior to eruption, imparting an additional mixing signature to the deposits.
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Forni, Francesca, Eleonora Petricca, Olivier Bachmann, Silvio Mollo, Gianfilippo De Astis, and Monica Piochi. "The role of magma mixing/mingling and cumulate melting in the Neapolitan Yellow Tuff caldera-forming eruption (Campi Flegrei, Southern Italy)." Contributions to Mineralogy and Petrology 173, no. 6 (May 3, 2018). http://dx.doi.org/10.1007/s00410-018-1471-4.
Повний текст джерела
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Landi, Patrizia, and Claudia D’Oriano. "The Onano eruption (Latera volcano, Central Italy): an example of magma mixing/mingling as dominant process in a caldera-forming eruption." Contributions to Mineralogy and Petrology 175, no. 9 (August 20, 2020). http://dx.doi.org/10.1007/s00410-020-01724-x.
Повний текст джерела
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Coombs, Michelle L., and Brian R. Jicha. "The eruptive history, magmatic evolution, and influence of glacial ice at long-lived Akutan volcano, eastern Aleutian Islands, Alaska, USA." GSA Bulletin, October 6, 2020. http://dx.doi.org/10.1130/b35667.1.
Повний текст джерелаАнотація:
New 40Ar/39Ar and whole-rock geochemical data are used to develop a detailed eruptive chronology for Akutan volcano, Akutan Island, Alaska, USA, in the eastern Aleutian island arc. Akutan Island (166°W, 54.1°N) is the site of long-lived volcanism and the entire island comprises volcanic rocks as old as 3.3 Ma. Our current study is on the 225 km2 western half of the island, where our results show that the focus of volcanism has shifted over the last ∼700 k.y., and that on occasion, multiple volcanic centers have been active over the same period, including within the Holocene. Incremental heating experiments resulted in 56 40Ar/39Ar plateau ages and span 2.3 Ma to 9.2 ka. Eruptive products of all units are primarily tholeiitic and medium-K, and range from basalt to dacite. Rare calc-alkaline lavas show evidence suggesting their formation via mixing of mafic and evolved magmas, not via crystallization-derived differentiation through the calc-alkaline trend. Earliest lavas are broadly dispersed and are almost exclusively mafic with high and variable La/Yb ratios that are likely the result of low degrees of partial mantle melting. Holocene lavas all fall along a single tholeiitic, basalt-to-dacite evolutionary trend and have among the lowest La/Yb ratios, which favors higher degrees of mantle melting and is consistent with the increased magma flux during this time. A suite of xenoliths, spanning a wide range of compositions, are found in the deposits of the 1.6 ka caldera-forming eruption. They are interpreted to represent completely crystallized liquids or the crystal residuum from tholeiitic fractional crystallization of the active Akutan magma system. The new geochronologic and geochemical data are used along with existing geodetic and seismic interpretations from the island to develop a conceptual model of the active Akutan magma system. Collectively, these data are consistent with hot, dry magmas that are likely stored at 5−10 km depth prior to eruption. The prolonged eruptive activity at Akutan has also allowed us to evaluate patterns in lava-ice interactions through time as our new data and observations suggest that the influence of glaciation on eruptive activity, and possible magma composition, is more pronounced at Akutan than has been observed for other well-studied Aleutian volcanoes to the west.
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Horn, Emma L., Rex N. Taylor, Thomas M. Gernon, Michael J. Stock, and E. M. Ruth Farley. "Composition and petrology of a mush-bearing magma reservoir beneath Tenerife." Journal of Petrology, September 26, 2022. http://dx.doi.org/10.1093/petrology/egac095.
Повний текст джерелаАнотація:
Abstract Deciphering the dynamics of sub-volcanic magmatic processes requires a detailed understanding of the compositional and textural relationships between melt and crystals. To examine these relationships, we investigated material from one of the largest caldera-forming explosive eruptions on the ocean island of Tenerife, the 312 ka Fasnia event. This eruption ejected juvenile pyroclasts of melt-bearing, partially crystalline cumulate nodules alongside phonolitic pumice and accidental lithic clasts. Nodules contain an average of 26% melt which is preserved as vesiculated and microcrystalline basanite in segregations, pathways and interstitial domains. Both the microcrystalline groundmass and crystal framework are generally unaltered as this crystal ‘mush’ remained supra-solidus until the eruption. We find no surficial or intrinsic evidence that the nodules were transported from their reservoir in a ‘carrier’ magma, and it is most likely that the mush was in situ when it was explosively fragmented and ejected during eruption. As such, the nodules preserve a record of the proportions and relationships between the crystal framework and pre-eruptive melt in an active magma mush reservoir; importantly, capturing a snapshot of the sub-volcanic system at a single point in time. We have analysed >100 of the mush nodules from the massive lithic breccia facies within the Fasnia Member of the Diego Hernández Formation. These cumulates span a diverse range of alkaline plutonic lithologies, from wehrlite and pyroxenite, through hornblende gabbros, to monzodiorite and syenite. Their textures record a range of crystallisation environments, including both crystal- and melt-rich groundmass domains, and invasion of near-solidus domains by ascending reactive melts. In addition, the cumulus phases record complex interactions between felsic and mafic magmas throughout their development, providing evidence for mush remobilization and disequilibrium. Relative homogeneity of melt compositions through the mafic and felsic lithologies testifies to melt mobility through the cumulates. Nevertheless, all melts are of different basanite-intermediate composition to the juvenile phonolitic pumice ejected during the same eruption. This observation implies that the mafic-felsic cumulate mush and the phonolite did not experience significant two-way mixing and existed as separate crustal reservoirs. However, the Fasnia eruption simultaneously fragmented and removed material from both reservoirs, implying the mafic system was subjacent to the felsic, but they did not form a contiguous body.
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Jolles, Jameson S. R., and Rebecca A. Lange. "Origin of Compositional Gradients with Temperature in the High-SiO2 Rhyolite Portion of the Bishop Tuff: Constraints on Mineral–Melt–Fluid Reactions in the Parental Mush." Journal of Petrology 62, no. 12 (October 22, 2021). http://dx.doi.org/10.1093/petrology/egab087.
Повний текст джерелаАнотація:
Abstract The Bishop Tuff (BT), erupted from the Long Valley caldera in California, displays two types of geochemical gradients with temperature: one is related to magma mixing, whereas the other is found in the high-SiO2 rhyolite portion of the Bishop Tuff and is characterized by twofold or lower concentration variations in minor and trace elements that are strongly correlated with temperature. It is proposed that the latter zonation, which preceded phenocryst growth, developed as a result of mineral–melt partitioning between interstitial melt and surrounding crystals in a parental mush, from which variable melt fractions were segregated. To test this hypothesis, trends of increasing vs decreasing element concentrations with temperature (as a proxy for melt fraction), obtained from published data on single-clast pumice samples from the high-SiO2 rhyolite portion of the Bishop Tuff, were used to infer their relative degrees of incompatibility vs compatibility between crystals and melt in the parental mush. Relative compatibility values (RCVi) for all elements i, defined as the concentration slope with temperature divided by average concentration, are shown to be linearly correlated with their respective bulk partition coefficients (bulk Di). Mineral–melt partition coefficients from the literature were used to constrain the average stoichiometry of the crystallization/melting reaction in the parental mush: 32 % quartz + 34 % plagioclase + 31 % K-feldspar + 1·60 % biotite + 0·42 % titanomagnetite + 0·34 % ilmenite + 0·093 % allanite + 0·024 % zircon + 0·025 % apatite = 100 % liquid. The proportions of tectosilicates in the reaction (i.e. location of eutectic) are consistent with depths of melt segregation of ~400–550 MPa and an activity of H2O of ~0·4–0·6. Temperatures of <770–780 °C are constrained by allanite in the reaction. Evidence that a fluid phase was present in the parental mush is seen in the decreasing versus increasing H2O and CO2 contents with temperature in the segregated interstitial melt that formed the high-SiO2 rhyolite portion of the Bishop Tuff. The presence of an excess fluid phase, which strongly partitions CO2 relative to the melt, is required to explain the compatible behavior of CO2, whereas the fluid abundance must have been low to explain the incompatible behavior of H2O. Calculated degassing paths for interstitial melts, which segregated from the parental mush and ascended to shallower depths to grow phenocrysts, match published volatile analyses in quartz-hosted melt inclusions and constrain fluid abundances in the mush to be ≤1 wt%. The source of volatiles in the parental mush, irrespective of whether it formed by crystallization or partial melting, must have been primarily from associated basalts, as granitoid crust is too volatile poor. Approximately twice as much basalt as rhyolite is needed to provide the requisite volatiles. The determination of bulk Di for several elements gives the bulk composition of the parental leucogranitic mush and shows that it is distinct from Mesozoic Sierran arc granitoids, as expected. Collectively, the results from this study provide new constraints for models of the complex, multi-stage processes throughout the Plio-Quaternary, involving both mantle-derived basalt and pre-existing crust, that led to the origin of the parental body to the Bishop Tuff.